The measurement of gas with solid particles therein and certain fluids which behave similarly, is of importance in many industries, e.g. chemical processing, food handling, transport loading and unloading, filtration, aeronautics and combustion fuel feeds. The above referenced patents have provided significant improvements in this general technical field.
Current flow measuring systems electrically connect the triboelectric sensor probe through an ultra low noise cable. The signal connection is fed to a core impedance conversion circuit (converter). A conversion circuit will amplify the input signal, where for the purposes of this invention amplification is defined broadly as voltage amplification, current amplification, impedance amplification (reduction) or combinations thereof. An over voltage protector is installed at the probe, and a current limiting barrier resistor before the converter's summing junction provides intrinsic safety for the probe and cable allowing the probe to be installed in hazardous environments.
Electrical offsets and drifts are of concern in the various circuits, and arrangements disclosed in the above referenced patents are used to compensate for these offsets and drifts. Other circuit implementations known in the art way also be used. Also various filters and other conditioning circuits, known in the art, may be used for noise elimination or other desired effects.
One of the continuing limitations of instrumentation, when practically applied in the above fields, to perform the measurement and feedback control of flow has been contamination of the physical probe. Any conductive substances, e.g. acids or other electrolytes, contained in the materials whose flow is being measured, may eventually build up providing electrical leakage paths which give rise to measurement errors. Also system errors occur as sensitivity (gain) and system zero change due to inexact temperature compensation, drift and/or other causes.
Old methods to solve this contamination problem have involved disassembly and cleaning or purging of the probe on a routine basis, and system calibration or other external testing circuits are used to monitor or measure system gain and zero. Employing these methods involves taking the system off-line and having skilled technicians perform the work.
It is an object of this invention to provide a circuit means which detects and quantifies, with the system on-line, when the probe is contaminated and needs cleaning.
It is another object of this invention to monitor and measure system gain and system zero while the system is on-line.
Another object of this invention is to minimize system down time and make efficient use of a technician's time.
It is an object of this invention that the probe-contamination, gain or zero change detection circuitry does not unduly interfere with or otherwise compromise the efficacy of the triboelectric detection instrumentation.